Train detection is the fundamental task of railroad signal and other systems. All other functions of a railroad signal system depend upon the system's ability to always and reliably detect a train moving within the limits of the system. The system must guarantee that a train moving within the limits of the system will be detected. Moreover, the system must be designed to verify that it is functioning as intended. In the event that an element of the system cannot perform its intended function, the system must revert to its safest condition. Information provided to train crews and motor vehicles by a signal system when it is at its safest or most restrictive condition is the message “STOP.” Signal engineers call devices and systems that incorporate these design requirements vital devices and describe them as fail-safe, meaning that they revert to their safest condition when they fail to or are unable perform their intended function. A fundamental principle of vital design for signal system electrical circuits is the closed circuit principle, which requires that the power source and return connections to an electrical device must be isolated and separate and any intervening control points within the circuit must treat both paths of the energy circuit. This assures that disruption/failure of either path will not violate the fail-safe principle. This essence of the closed circuit principle is that any element of a vital circuit must function separately and independently from other circuit elements—vital circuits may not share circuit elements that afford alternative energy or logic paths that would allow the system to violate the fail-safe principle. Microprocessor-based signal system elements satisfy the closed circuit principle by using hardware that is operationally independent and application logic that requires redundant and independent processing of all data necessary to the fail-safe operation of the device. If the direct physical connection cannot comply with the closed circuit principle, it must comply with a vital communications protocol. A vital communications protocol can be used to verify the integrity and operational status of the elements of the communication means. Verification must be sufficient to ensure that, in the event of a communications failure, the communicating devices will not violate the fail-safe principle.
Apparatus, methods, systems, techniques, etc. that provide vital, reliable, and efficient train detection that is independent of the track structure would represent a significant advancement in the art. It would be a further advancement to have such the elements of such detection systems communicate with each other using vital wireless communication protocols. It would be a further advancement to have the elements of such detection systems be power efficient, small size, modular, capable of rapid installation and easily reconfigurable. It would be a further advancement to have such detection systems combine magnetic field sensing, power efficient microprocessors, and wireless communications to detect train event data sequences and determine unique train identification signatures based upon the distortion of the local magnetic field by railcars moving within range of a sensor. It would be a further advancement in the art to identify individual trains, to recognize complex movement patterns and to verify identity, location and movement of individual trains over a variety of locations. Such advances will improve safety, and enhance the operation of train control signal systems and highway crossing signal devices.